Denning served on board the U.S. Picket Boat No. 1 in action, 27 October 1864, against the Confederate ram Albemarle which had resisted repeated attacks by our steamers and had kept a large force of vessels employed in watching her. The picket boat, equipped with a spar torpedo, succeeded in passing the enemy pickets within 20 yards without being discovered and then made for the Albemarle under a full head of steam. Immediately taken under fire by the ram, the small boat plunged on, jumped the log boom which encircled the target and exploded its torpedo under the port bow of the ram. The picket boat was destroyed by enemy fire and almost the entire crew was taken prisoner or lost.